The invention relates to an electrophotographic copying machine, and more specifically, to a developing unit of the magnetic brush type for use in an electrophotographic copying machine of the kind in which an electrostatic latent image is formed on a drum surface in accordance with the image of an original and is then developed with a developer.
A developing unit of magnetic brush type essentially comprises a magnet, a sleeve surrounding the magnet and a developer. A magnetic brush comprising the developer is formed on the outer peripheral surface of the sleeve and is brought into rubbing contact with a drum surface to develop an electrostatic latent image formed on the drum surface. Of significance in an electrophotographic copying machine with magnetic brush developing is the relative positional relationship between the drum surface on which the latent image is formed and the developing unit or more specifically the magnetic brush, which relationship has a great influence upon the image quality of a copy obtained. Specifically, the spacing between the drum and the magnetic brush must be maintained constant along the length of the central axis of rotation, otherwise a non-uniformity is produced in the optical density of the resulting image.
On the other hand, the drum and/or developing unit is frequently disassembled from the body of the copying machine for the purpose of maintenance and inspection of these components as well as other devices which are associated with them. Thus, there must be some provision to assure a uniform spacing between the drum and the magnetic brush when these components are assembled together again.
The spacing between the drum and the magnetic brush is usually adjusted by moving the magnetic brush toward or away from the drum. However, because the adjustment is referenced to a side plate of the developing unit or outer walls of the copying machine, the reference of the adjustment varies from machine to machine. This implies that when a developing unit is replaced by a fresh one, the spacing between the drum and the brush must be adjusted again. The same discussion applies to a developing unit in which a plurality of magnetic brushes are formed. In this instance, the individual magnetic brushes have to be adjusted in order to maintain a given spacing between the individual brushes and between each brush and the drum. This requires a considerable length of time for the maintenance and inspection of the machine.